Synthesis of a derivative of α-D-Glcp(1->2)-D-Galf suitable for further glycosylation and of α-D-Glcp(1->2)-D-Gal, a disaccharide fragment obtained from varianose

• Carla Marino,
• Carlos Lima,
• Karina Mariño and
• Rosa M. de Lederkremer

Beilstein J. Org. Chem. 2012, 8, 2142–2148, doi:10.3762/bjoc.8.241

• lactone, due to the differential reactivity of the HO groups [21][22]. These derivatives can be used as acceptors, with the anomeric center virtually masked as a carbonyl group, which may be later selectively reduced to the hemiacetal with diisoamylborane (DSB). By this strategy the synthesis of many

Organocatalytic cascade aza-Michael/hemiacetal reaction between disubstituted hydrazines and α,β-unsaturated aldehydes: Highly diastereo- and enantioselective synthesis of pyrazolidine derivatives

• Zhi-Cong Geng,
• Jian Chen,
• Ning Li,
• Xiao-Fei Huang,
• Yong Zhang,
• Ya-Wen Zhang and
• Xing-Wang Wang

Beilstein J. Org. Chem. 2012, 8, 1710–1720, doi:10.3762/bjoc.8.195

• /hemiacetal sequence with chiral or achiral secondary amines as organocatalysts. Thus, a series of achiral pyrazolidine derivatives were obtained with good yields (up to 90%) and high diastereoselectivities (>20:1) with pyrrolidine as an organocatalyst, and enantioenriched pyrazolidines are also achieved with

• stereoselective cascade reaction for the synthesis of the pyrazolidine compounds through organocatalysis. In this paper, we present a convenient access to racemic and enantioenriched 5-hydroxypyrazolidines through a domino aza-Michael/hemiacetal organocatalytic sequence of disubstituted hydrazines to α,β

• aldehydes containing only linear alkyl chains, whereas our work provides better results when unsaturated aldehydes bearing an aromatic moiety are employed. Results and Discussion First, the cascade aza-Michael/hemiacetal reactions between disubstituted hydrazines 2a–c and 4-nitrocinnamaldehyde (3a) were

The Amadori rearrangement as glycoconjugation method: Synthesis of non-natural C-glycosyl type glycoconjugates

• Katharina Gallas,
• Gerit Pototschnig,
• Florian Adanitsch,
• Arnold E. Stütz and
• Tanja M. Wrodnigg

Beilstein J. Org. Chem. 2012, 8, 1619–1629, doi:10.3762/bjoc.8.185

• products featuring a secondary amine at position C-1, compounds 24 and 25, were further reacted with triphosgene [25]. In this reaction, the anomeric hydroxy group and the amine at position C-1 formed a cyclic carbamate, thereby stabilising the hemiacetal at the anomeric position. Compounds 24 (a and b

Stereoselective synthesis of trans-fused iridoid lactones and their identification in the parasitoid wasp Alloxysta victrix, Part II: Iridomyrmecins

• Robert Hilgraf,
• Nicole Zimmermann,
• Lutz Lehmann,
• Armin Tröger and
• Wittko Francke

Beilstein J. Org. Chem. 2012, 8, 1256–1264, doi:10.3762/bjoc.8.141

• that, the cis-fused nepetalactone 15 and diastereomers thereof are typical components of many species of the plant genus Nepeta [22][23]. Along with the corresponding hemiacetal 16, which shows (1R)-configuration, 15 is also a most important sex pheromone of aphids [24] (Figure 8). Nevertheless

Synthesis of 4” manipulated Lewis X trisaccharide analogues

• Christopher J. Moore and
• France-Isabelle Auzanneau

Beilstein J. Org. Chem. 2012, 8, 1134–1143, doi:10.3762/bjoc.8.126

• , trichloroethyl galactoside 16 was converted to the trichloroacetimidate donor 9 in two steps: the anomeric trichloroethyl group was removed (Zn/AcOH), and then the resulting hemiacetal was treated with trichloroacetonitrile in the presence of DBU giving the desired α-trichloroacetimidate in good yield. A

Synthesis of a library of tricyclic azepinoisoindolinones

• Bettina Miller,
• Shuli Mao,
• Kara M. George Rosenker,
• Joshua G. Pierce and
• Peter Wipf

Beilstein J. Org. Chem. 2012, 8, 1091–1097, doi:10.3762/bjoc.8.120

• . When the RCM reaction of 7 was conducted on larger scale in the absence of Ti(OiPr)4, and the crude intermediate was subjected to m-CPBA oxidation, epoxy alcohol 6 was isolated in 11% overall yield. LC–MS as well as NMR analyses suggested a 5:1 ratio of epimers at the hemiacetal carbon. Hydroxylation

Branching out at C-2 of septanosides. Synthesis of 2-deoxy-2-C-alkyl/aryl septanosides from a bromo-oxepine

• Supriya Dey and
• Narayanaswamy Jayaraman

Beilstein J. Org. Chem. 2012, 8, 522–527, doi:10.3762/bjoc.8.59

• been explored in many instances, for example, (i) hemiacetal or acetal formation from a linear precursor containing aldehyde and an appropriately positioned hydroxyl group [4][5][6][7][8]; (ii) Knoevenagel-type condensation of sugar aldehyde with active methylene compounds [9][10]; (iii) ring-closing

Metathesis access to monocyclic iminocyclitol-based therapeutic agents

• Ileana Dragutan,
• Valerian Dragutan,
• Carmen Mitan,
• Hermanus C.M. Vosloo,
• Lionel Delaude and
• Albert Demonceau

Beilstein J. Org. Chem. 2011, 7, 699–716, doi:10.3762/bjoc.7.81

• in both the α- and β-forms, each of which is responsible for inhibition of α- or β-glucosidase, respectively. Similar to its other congeners, mannonojirimycin (60; MJ or nojirimycin B) and galactonojirimycin (61; GJ or galactostatin), nojirimycin is unstable because hemiacetal structures can be

The arene–alkene photocycloaddition

• Ursula Streit and
• Christian G. Bochet

Beilstein J. Org. Chem. 2011, 7, 525–542, doi:10.3762/bjoc.7.61

• afforded the hemiacetal after spontaneous cyclization. Subsequent oxidation and deprotection afforded the desired compound. In the same paper, the total synthesis of the naturally occurring epimer of Penifulvin B (Penifulvin C) was described, which was achieved by replacing the trans-olefin by the cis

Addition of lithiated enol ethers to nitrones and subsequent Lewis acid induced cyclizations to enantiopure 3,6-dihydro-2H-pyrans – an approach to carbohydrate mimetics

• Fabian Pfrengle and
• Hans-Ulrich Reissig

Beilstein J. Org. Chem. 2010, 6, No. 75, doi:10.3762/bjoc.6.75

• -methylmorpholinoxide-system afforded α-hydroxyketone 9 via in situ hydrolysis of an initially formed hemiacetal. Bromination with NBS in MeCN/H2O led to α-bromoketone 10 and its desilylated derivative 11 as single diastereomers. We presume that the NBS attacks the enol ether moiety, as is also the case with the

• conditions were applied to the diastereomeric dihydropyran trans-5a, different behaviour was noted (Scheme 6). A smooth hydrolysis of the enol ether moiety leading to ketone 12 was neither feasible with methanolic HCl nor with aqueous HCl. After dihydroxylation, a partial hydrolysis of the hemiacetal

Benzyne arylation of oxathiane glycosyl donors

• Martin A. Fascione and
• W. Bruce Turnbull

Beilstein J. Org. Chem. 2010, 6, No. 19, doi:10.3762/bjoc.6.19

• -hemiacetal 22 was isolated in 70% yield following purification by flash silica chromatography [30]. Cleavage of the acyclic O-2 ketal on glycosyl acetate 21, followed by acetyl transfer from O-1 to O-2 could account for this transformation [31]. Arylation/acetate glycosylation using oxathiane ether donor 17

Convergent syntheses of Le^X analogues

• An Wang,
• Jenifer Hendel and
• France-Isabelle Auzanneau

Beilstein J. Org. Chem. 2010, 6, No. 17, doi:10.3762/bjoc.6.17

• situ by adding water to the reaction mixture. The resulting triacetate was chloroacetylated at O-3 and the resulting fully protected thioglycoside 23 was converted to the corresponding hemiacetal that was, in turn, treated with trichloroacetonitrile and DBU to give the α-trichloroacetimidate galactosyl